Various movable clamping facilities have been known, for example chain conveyors consisting of several parallel-extending chains with drivers, against which the bole is pressed by hold-downs. Slides guided in suspension tracks are frequently employed, seizing the bole at both ends at the front face with disks that can be hydraulically brought into pressure contact and are studded with pins penetrating into the wood. These holding disks are supported at the slide frame to be rotatable and lockable in several positions so that the bole, after each passage past the machining tools, can be swung about its longitudinal axis into a desired angular range. Thereby, four-sided or multiple-sided beams, boards or planks can be cut. This readily operable and versatile workpiece loading facility is, however, also burdened by restrictive drawbacks due to the fact that the bole is freely suspended between its end-side clamping points and shows a marked sag in case of relatively long lengths. Furthermore, vibrations occur in the central zone of the bole leading to great stress, depending on the tool utilized, and resulting in rough cutting surfaces. This fixture can thus be used only for relatively short logs. Also, high-power tools, such as chippers (rotary milling cutters) cannot be employed since the stresses occurring in such a case are too high to be controlled by this device.
A further disadvantage resides in that the clamping disks must have a relatively large diameter in order to ensure adequate hold. The size of the holding disks, however, limits the region of the bole that can be machined. Boards or planks can be cut only from the marginal zones; the clamped-in-place region, covered by the retaining disk, must be processed into beams or must be further machined in a finishing saw facility.
DOS 1,503,923 discloses a clamping device for tree logs using trolleys for retaining means, the log being carried by supports made up of rollers. The guidance of the log while moving past machining tools is unsatisfactory with the known clamping device so that poor cuts are the result.
DOS 3,709,240 describes a holding device consisting of a laterally guided, low beam and clamping arms guided independently of this beam on a vertically adjustable carrier by means of a top rail. This holding device does not ensure an adequately accurate guidance, either, for a bole while moving past a machining station.